This research proposal is concerned with the auditory and phonetic coding processes that constitute the early perceptual analysis of a speech signal. Experimental procedures involving identification, discrimination, detection, reaction time and dichotic listening will be used in conjunction with natural speech, synthetic speech and complex nonspeech stimuli. Additional studies will use stimuli that are ambiguous between speech and nonspeech. These studies will test current theories of speech perception and aid in outlining the processes and flow of information in the early auditory to phonetic coding of speech. Experiments will examine the role of auditory coding processes in speech perception. Some experiments are designed to investigate which aspects of phonetic distinctions are mediated by auditory processes. Other experiments will examine acoustic invariants that have been proposed for phonetic distinctions and investigate their role in perception. Experiments on phonetic coding and other language specific processing will investigate the role of coarticulatory knowledge and other abstract representations (phonological, syllabic) on speech perception. Experiments on the combined effects of auditory and phonetic coding will investigate the nature of the pervasive contrast effects that are found in identification tasks. Using both speech and nonspeech stimuli, the relationship between the mode of processing (auditory versus phonetic) and contrast effects will be explored along with the roles of an internal phonetic representation and its degree of match to various stimuli in determining contrast effects. New studies on individual differences in dichotic listening will also be undertaken to investigate a possible link between speech production and perception and its role in the auditory to phonetic coding of speech. The results of these studies will be used to refine and elaborate an information processing model of speech perception that has been implemented as a computer simulation. This model can serve as a normative base against which theories (and data) on developmental processes and disorders can be compared.